Method and Apparatus for Locating the Surface of Solid Growth Culture Media in a Plate

ABSTRACT

A method for locating the surface of a solid growth culture medium in a plate in a plate work position, the plate work position including a sensor and having a datum level fixed in one dimension (z), the method including: ˜placing the plate in the plate work position; ˜using the sensor to sense the medium surface for the positioned plate and measuring the distance to the medium surface; and ˜referencing the measured distance to the datum level to determine a surface positional reference, relative to the datum level, in one dimension (z) for the surface of the medium in the positioned plate.

This international patent application claims priority from Australianprovisional patent application 2007900147 filed on 12 Jan. 2007, thecontents of which are to be taken as incorporated herein by thisreference.

FIELD OF THE INVENTION

The present invention relates generally to apparatus involved in theinoculation of solid growth culture media with a microbiological sample,and the subsequent streaking of the inoculum to produce isolatedbacterial colonies, principally for diagnostic purposes in a laboratory,such as for medical diagnostic purposes. The present inventionspecifically relates to a method and an apparatus for locating thesurface of a solid growth culture medium in a plate, to assist with asubsequent streaking operation, in an automated streaking apparatus.However, the invention is not to be limited to only that application.

BACKGROUND OF THE INVENTION

The isolation of individual colonies of micro-organisms (and inparticular bacteria) is an important procedure in many microbiologicallaboratories. Traditionally, this isolation of bacteria has beenperformed manually by skilled laboratory technicians who first dispensea microbiological sample onto the surface of a solid growth culturemedium, such as agar in a Petri dish (which will hereafter simply bereferred to as a “medium” in an “agar plate” or simply in a “plate”),followed by the use of a hand-tool to spread the sample across thesurface of the medium (called “streaking”).

The hand-tool typically includes a terminal loop to make multiplestreaks of increasing dilution of the inoculum across the medium. Thestreaks of increasing dilution tend to provide, generally towards thetail of the streaks, a number of single cells that allow for the growthof isolated microbiological colonies after incubation. These isolatedcolonies may then be analysed for colony morphology, and may undergostaining and other procedures which are necessary for determining, forexample, the genus, the species and the strain of the previouslyunidentified organism.

Such inoculation and streaking is highly repetitious and in manypathology diagnostic microbiology laboratories is usually conducted invery high volumes, such as in volumes as high as 1,000 to 15,000 platesper day. It is tedious and laborious work that therefore is prone toerror and inaccuracies. It is quite obviously work that would lenditself to either partial or full automation.

The literature is replete with suggestions for how best to automatethese laboratory functions, yet very few of these suggestions have everactually found success in a commercial laboratory environment. Ittherefore appears that the successful enablement of suitable laboratoryapparatus has to date, for most, proved elusive.

Three recent suggestions for the automation of these laboratoryfunctions can be found in the following documents; U.S. Pat. No.4,981,802 (C. Wylie et al) titled “Method and Apparatus for Streaking aCulture Medium”, U.S. Pat. No. 6,617,146 (F. Naccarato et al) titled“Method and Apparatus for Automatically Inoculating Culture Media WithBacterial Specimens From Specimen Containers”, and international patentpublication WO2005/071055 (Medvet Science Pty Ltd) titled “MicrobialStreaking Device” (licensed to the present applicant).

The Wylie and Naccarato patents describe automated and semi-automatedapparatus that utilize re-usable streaking tools similar to the handstreaking tools mentioned above, without describing a suitable system ormechanism for that apparatus to determine, in three dimensional space,the precise location of the surface of the medium.

While the Medvet Science publication describes the use of a new form ofstreaking tool, being a streaking applicator that includes a line ofspaced apart contact surfaces (for contact with the surface of solidgrowth media), the contact surfaces being resiliently flexibly supportedby a common support member, this new streaking tool still of courserequires placement upon the surface of the medium. The Medvet Sciencepublication suggests that this can be dealt with providing the apparatuswith a pressure sensing device to determine when the tool is suitablyupon the surface.

It will be appreciated that the height of medium, such as agar, within aplate will fluctuate depending upon many factors. For example, not onlydo different plate and solid growth culture medium suppliers invariablyproduce agar plates, for example, with a wide variety of surface heightsfrom one supplier to the next, but even the same suppliers tend tosupply their own plates with varying heights of media. Also, differentcompositions and ages of media used for this purpose tend also toproduce plates with different media surface heights. Therefore, and dueto such fluctuations in height, it is generally not possible for anautomated streaking apparatus to rely upon the height of the surface ofmedia in all plates to be the same.

It is therefore not feasible for an inoculating device, for example, ofsuch an automated apparatus to rely on being able to place inoculum uponthe surface of media at the same location in three dimensional space forevery plate to be processed thereby, and significant difficulties andcomplexities can be introduced in an apparatus that does. As anotherexample, there are also potential difficulties and complexities for astreaking device of such an automated apparatus in trying to place astreaking tool upon the surface (so as to spread the inoculum ratherthan to gouge the surface) of media at the same location for every platein three dimensional space.

In relation to an inoculating device, it will be appreciated that theincorrect location of a dispensing tip in the z dimension (height) willgive rise to the inoculum being dispensed from too high (and thus notdispensing as required), or there being contact with the surface suchthat the tip gouges the surface of the medium. In relation to astreaking device, incorrect location of the contact surfaces in the zdimension (height) will give rise to there either being no contact withthe inoculum whatsoever, or there being too much contact such that thestreaking tool also gouges tracks in the surface of the medium.

It is an aim of the present invention to provide both a method and anapparatus capable of locating the surface of the medium in a plate priorto, for example, inoculation and streaking of that plate. In thisrespect, and as foreshadowed above, it is also an aim of the presentinvention for the method and apparatus to find use in laboratorysituations other than the inoculation and streaking situations describedabove. Indeed, the method and apparatus of the present invention mayfind use in any laboratory to simply provide a process, for any purpose,for locating the surface of solid growth culture medium in a plate.

Before turning to a summary of the present invention, it must beappreciated that the above description of the prior art has beenprovided merely as background to explain the context of the invention.It is not to be taken as an admission that any of the material referredto was published or known, or was a part of the common general knowledgein Australia or elsewhere.

It is also useful to provide an explanation of some of the terms thatwill be used to define the spatial relationship of the apparatus andvarious parts thereof. In this respect, spatial references throughoutthis specification will generally be based upon a plate ultimately beinginoculated and streaked in an automated streaking apparatus in anupright orientation, with the surface of the medium in the plate beinggenerally flat and horizontal. With this environment as the basis, theapparatus and some parts thereof may then be defined with reference tothe “horizontal”, allowing further references to “upper” or “upwardly”and “lower” or “downwardly”, and also to the “vertical”. In thisrespect, the traditional geometric spatial reference to x,y and zdimensions, and then to the x direction (or axis), the y direction (oraxis) and the z direction (or axis), will also be adopted, with the xand y directions lying generally horizontally and the z direction lyinggenerally vertically.

Finally, some aspects of the present invention that may ultimately beclaimed in isolation (and not in an in-use environment), may nonethelessbe difficult to describe and understand in isolation. Thus, some of thefollowing description does describe the invention and its embodiments insuch an in-use environment (for example, in association with a platecarrying medium within an automated streaking apparatus). Of course, itmust be appreciated that the use of such description, and the use of theabovementioned spatial relationships, to define the present invention,is not to be seen as a limitation and certainly is not to be seen as alimitation only to the in-use environment, unless that intention isclearly stated.

SUMMARY OF THE INVENTION

The present invention provides a method for locating the surface of asolid growth culture medium in a plate in a plate work position, theplate work position including a sensor and having a datum level fixed inone dimension (z), the method including:

-   -   placing the plate in the plate work position;    -   using the sensor to sense the medium surface for the positioned        plate and measuring the distance to the medium surface; and    -   referencing the measured distance to the datum level to        determine a surface positional reference, relative to the datum        level, in one dimension (z) for the surface of the medium in the        positioned plate.

It will thus be appreciated that the surface of a medium in a plate,which plate is in its normal, generally horizontal orientation, can thusbe located in at least the z dimension by virtue of the determination ofthe surface positional reference. This effectively determines the heightof the medium in the plate, at least with reference to the datum level.In a preferred form, the datum level will be a level (or a surface) thatforms a part of a plate platform upon which the plate can be clamped andsupported. Therefore, in this preferred form, the determination of thesurface positional reference effectively determines the height of themedium with reference to the plate platform upon which it rests. This isuseful in that the referencing of the medium in this manner then permitsanother, possibly unrelated, apparatus to operatively interact with thesurface of the medium with some precision, as would be required wherethe invention is used in an automated streaking apparatus (as will beoutlined below).

In one form of the invention, the medium height is not sensed by thesensor across its full extent, but is only sensed in a sensing regionwhich is a part of that full extent. For example, in one form, themethod senses the medium surface within a sensing region and measuresthe distance to the medium surface within that sensing region. Inpractice, this measured distance is likely to be an average over thearea of the sensing region, given the likelihood of the distance varyingacross that region due to the height of the surface varying due tosurface imperfections and the like.

However, and as mentioned above, a preferred use for the method of thepresent invention is in the inoculation and streaking of the medium inthe plate, which generally requires the determination of the location inthree dimensional space of a line across the surface of the medium, andnot just the determination of a point (or region) in one dimensionalspace, for the purpose of spreading an inoculum along that line and thenlocating a streaking tool along that line (sometimes referred to as an“action line”).

The present invention thus also provides a method for locating thesurface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and having anotional action line fixed in two dimensions (x,y) in a predeterminedposition and having a datum level fixed in one dimension (z), the methodincluding:

-   -   placing the plate in the plate work position;    -   using the sensor to sense the medium surface within a sensing        region for the positioned plate and measuring an average        distance to the medium surface within that sensing region;    -   referencing the measured distance to the datum level to        determine a surface positional reference relative to the datum        level in one dimension (z) for the surface of the medium in the        positioned plate; and    -   using the surface positional reference and the notional action        line to determine a line in three dimensions (x,y,z) that is        representative of a line across the surface of the medium in the        positioned plate.

In another preferred form of the present invention, the method includesthe additional step of setting an upper detection limit and a lowerdetection limit, in some forms with the upper detection limit above thedatum level and the lower detection limit below the datum level, todefine a detection range between the upper and lower limits. The use ofsuch a detection range can be adopted in conjunction with either themethod for the determination of the surface positional reference aloneor the method for the determination of the representative surface linefrom the surface positional reference.

A detection range of this type is an arbitrary range and thus the upperand lower limits of the detection range can be set arbitrarily. Adetection range can provide a calibration opportunity and allows theidentification of, for example, multiple calibration sub-ranges to beapplied within the detection range. For example, in some forms of theinvention it may not be necessary or desirable for the method to be ableto determine if a plate positioned in the plate work position stillincludes its lid thereon, or perhaps has been placed in the plate workposition upside down. Thus, by adopting a narrow detection range, wherethe upper limit is only just above where the surface of the medium isexpected to be, and the lower limit is only just below where the surfaceof the medium is expected to be, the sensor will not function if thedetectable height of the plate in the plate work position is outsidethis narrow range, due to the sensor detecting either the surface of theplate lid or the surface of the plate bottom.

Conversely, there may be situations where it is desirable for the methodto be able to provide an alarm, for example, if a lidded or empty plateis placed in the plate work position. If a suitably broad enoughdetection range has been set, the sensor will thus sense the presence ofthe lid wall or the bottom wall, and will measure the distance to thatsurface rather than to the surface of medium in the plate. Thus, by theprovision of a suitably broad detection range with calibrationsub-ranges for alarm conditions (lidded plate or empty plate, forexample) and for non-alarm conditions (de-lidded upright plate), thecalibration sub-ranges can cause the identification (by virtue of thedetermination of the surface positional reference and its presence inone of the alarm calibration sub-ranges) of an alarm condition, as wellas allow for the proper functioning of the method.

For example, and depending upon the likely thicknesses of plates and thelikely height of the medium used therein, in one form the detectionrange can be set at about 30 mm, with the upper limit set 20 mm abovethe datum level and the lower limit set 10 mm below the datum level. Inthis form, and with reference to typical plates, a lidded plate (ineither orientation) may produce a surface positional reference at about7 mm below the upper limit, a de-lidded upright plate may produce asurface positional reference (for its medium surface) at about 14 mmbelow the upper limit, and a de-lidded but empty plate may produce asurface positional reference at about 18 mm below the upper limit (whichis only the thickness of the bottom wall of the plate above the datumlevel).

The present invention thus also provides a method for locating thesurface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and having a datumlevel fixed in one dimension (z), the method including:

-   -   setting an upper limit and a lower limit to define a detection        range between the upper and lower limits;    -   placing the plate in the plate work position;    -   using the sensor to sense, within the detection range, the        medium surface for the positioned plate and measuring the        distance to the medium surface; and    -   referencing the measured distance to the datum level to provide        a surface positional reference relative to the datum level in        one dimension (z) for the surface of the medium in the        positioned plate.

Further, the present invention may also provide a method for locatingthe surface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and having anotional action line fixed in two dimensions (x,y) in a predeterminedposition and having a datum level fixed in one dimension (z), the methodincluding:

-   -   setting an upper limit and a lower limit to define a detection        range between the upper and lower limits;    -   placing the plate in the plate work position;    -   using the sensor to sense the medium surface, within the        detection range, within a sensing region for the positioned        plate and measuring an average distance to the medium surface        within that sensing region;    -   referencing the measured distance to the datum level to        determine a surface positional reference relative to the datum        level in one dimension (z) for the surface of the medium in the        positioned plate; and    -   using the surface positional reference and the notional action        line to determine a line in three dimensions (x,y,z) that is        representative of a line across the surface of the medium in the        positioned plate.

As mentioned above, preferably the datum level is fixed and is thus aknown parameter in the apparatus. In one form of the invention, thedatum level is fixed as the uppermost surface of a platform configuredto hold the plate in the plate work position, the uppermost surface thusbeing that surface immediately below the plate. With this in mind, theplatform is itself preferably fixed in the z direction, such that itslocation in the z direction is constant and known, regardless of whetherthe platform is required to move in the x or y directions as a part ofits normal operation.

It may thus be beneficial to further include as a part of the presentinvention, an ability to regularly verify that this location has notaltered, such as by being able to verify this on a daily, weekly ormonthly basis, or being able to verify this prior to every operationalrun of the method and apparatus of the invention, or even prior to(although this is unlikely) each measurement being taken. Indeed, itwill be appreciated that even normal mechanical operational vibrations(or temperature variations) may cause the location of the datum level inthe z direction to alter (even slightly alter), which could have animpact on the precision of operation of the method and apparatus.

The sensor can be any type of sensor that is able to be programmed andcontrolled to sense the presence of a surface in the manner describedabove and then to measure the distance to the sensor, ideally from afixed datum point that is a part of the sensor. The sensor may forexample be a laser sensor or an ultrasonic sensor. Preferably, thesensor includes a programmable controller that is able to additionallyperform the referencing tasks mentioned above.

In a preferred form, the sensor is an ultrasonic sensing device thatincludes an ultrasonic beam focusing element that is capable ofproviding a focused beam on the medium surface, preferably within thesensing region mentioned above. In the form of the invention where therepresentative line is to be determined from the surface positionalreference, this sensing region is thus preferably central to thepredetermined notional action line also mentioned above.

The sensor is preferably rigidly mounted to a main frame, therebydefining the general location of the plate work position. In this form,the sensor is ideally mounted so that it is above the plate workposition and is operatively adjacent a positioned plate held immediatelytherebelow in a plate platform, the positioned plate having its mediumsurface open upwardly.

Thus, the present invention also provides an apparatus for locating thesurface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and having a datumlevel fixed in one dimension (z), wherein the sensor is capable ofsensing the medium surface for the positioned plate and measuring thedistance to the medium surface, the apparatus also including means forreferencing the measured distance to the datum level to determine asurface positional reference, relative to the datum level, in onedimension (z) for the surface of the medium in the positioned plate.

The present invention further provides an apparatus for locating thesurface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and having anotional action line fixed in two dimensions (x,y) in a predeterminedposition and having a datum level fixed in one dimension (z), whereinthe sensor is capable of sensing the medium surface within a sensingregion for the positioned plate and measuring an average distance to themedium surface within that sensing region, the apparatus also includingmeans for referencing the measured distance to the datum level todetermine a surface positional reference relative to the datum level inone dimension (z) for the surface of the medium in the positioned plateand then using the surface positional reference and the notional actionline to determine a line in three dimensions (x,y,z) that isrepresentative of a line across the surface of the medium in thepositioned plate.

Further, the present invention also provides an apparatus for locatingthe surface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and having a datumlevel fixed in one dimension (z), wherein the sensor has an upper limitand a lower limit to define a detection range between the upper andlower limits, and is capable of sensing, within the detection range, themedium surface for the positioned plate and measuring the distance tothe medium surface, the apparatus including means for referencing themeasured distance to the datum level to provide a surface positionalreference relative to the datum level in one dimension (z) for thesurface of the medium in the positioned plate.

Further still, the present invention may also provide an apparatus forlocating the surface of a solid growth culture medium in a plate in aplate work position, the plate work position including a sensor andhaving a notional action line fixed in two dimensions (x,y) in apredetermined position and also having a datum level fixed in onedimension (z), wherein the sensor has an upper limit and a lower limitto define a detection range between the upper and lower limits, and iscapable of sensing the medium surface, within the detection range,within a sensing region for the positioned plate and measuring anaverage distance to the medium surface within that sensing region, theapparatus including means for referencing the measured distance to thedatum level to determine a surface positional reference relative to thedatum level in one dimension (z) for the surface of the medium in thepositioned plate, and then using the surface positional reference andthe notional action line to determine a line in three dimensions (x,y,z)that is representative of a line across the surface of the medium in thepositioned plate.

Also, it will of course be appreciated that the surface positionalreference, and the representative line, for the surface of a medium in apositioned plate will be specific to the medium in that positioned plateonly, and may be (and is actually likely to be) a different surfacepositional reference and representative line compared to the surface ofthe next plate processed in the plate work position.

Finally, it is envisaged that the method and apparatus of the presentinvention will additionally find use with half-plates (often referred toas bi-plates) where the two halves of a plate are separated by anupstanding diametric wall, and each half containing a medium whoseheight is to be determined in the manner described above. In thissituation, the methods described above can be modified to also permitdetection of, or confirmation of, the location of the upstanding wall,to then trigger the operation of the method of the invention twice inrelation to that plate, on both halves. Alternatively, the method couldof course be modified to simply permit the apparatus to be otherwiseinformed of the existence of a bi-plate, to subsequently triggeroperation of the method on both halves.

As evident from the above, the method and apparatus of the presentinvention is primarily suitable for use with an automated streakingapparatus, ideally of the type generally described in the presentapplicant's international patent application filed on 11 Jan. 2008titled “Method and Apparatus for Inoculating and Streaking a Medium in aPlate”, claiming priority from Australian provisional patent application2007900146, the full content of which is hereby incorporated byreference. For present purposes, one form of that streaking apparatusgenerally includes:

-   -   (a) a plate supply capable of storing raw plates in an inverted        orientation;    -   (b) a plate transfer feed mechanism capable of obtaining an        inverted raw plate from the plate supply, de-lidding the raw        plate and orientating the raw plate such that its bottom is        lowermost, and transferring the orientated and de-lidded raw        plate to a plate work position in an inoculating and streaking        station;    -   (c) the apparatus of the present invention, being a sensor        capable of locating the surface of the medium in a positioned        plate prior to inoculation and streaking of that plate;    -   (d) an inoculating device capable of dispensing inoculum on the        surface of the medium in the positioned plate;    -   (e) a streaking device capable of obtaining a streaking        applicator from a streaking applicator supply and then moving        the streaking applicator such that its line of spaced apart        contact surfaces contacts the surface of the medium in the        positioned plate, prior to rotation of the positioned plate for        streaking;    -   (f) a plate store capable of storing processed plates in an        inverted orientation; and    -   (g) a plate transfer store mechanism capable of retrieving a        processed plate from the plate work position, re-orientating and        re-lidding the processed plate, and transferring the processed        plate to the plate store.

Thus, in one form (although not the only form thereof), the method andapparatus of the present invention is intended to be suitable for use asthe sensor for the plate work position of the above described automatedstreaking apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Having briefly described the general concepts involved with the presentinvention, a preferred embodiment will now be described that is inaccordance with the present invention. However, it is to be understoodthat the following description is not to limit the generality of theabove description.

In the drawings:

FIG. 1 is a perspective view from above of an apparatus in accordancewith a preferred embodiment of the present invention, showing a plateplatform near a plate work position;

FIG. 2 is a perspective view from above of the apparatus of FIG. 1,showing a plate held in the plate platform in the plate work position;

FIG. 3 is a perspective view from above of a part of the apparatus ofFIG. 1, showing the apparatus in use and a three dimensional actionline; and

FIG. 4 is a schematic illustration of the apparatus of FIG. 1 in use,showing the various geometric and mathematical relationships.

DESCRIPTION OF A PREFERRED EMBODIMENT

Illustrated in FIGS. 1 and 2 is an apparatus 10 for locating the surfaceof a solid growth culture medium 12 having a surface 13 in a plate 14 ina plate work position A, with the medium 12 and the plate 14 not shownin FIG. 1. FIG. 1 shows a plate platform 30 able to receive a plate 14in a centralized and clamped position in order to move the plate in thedirection of arrow X into the plate work position A. The plate platform30 is mounted on a support 31 for sliding movement along a guide rail 33in response to suitable controllers. The plate platform 30 includes aplate clamping member 32 in the form of three movable lugs operated by acamming device (not shown), which lugs are preferably also able tofunction as a plate centralizing means for centralizing the position ofthe plate 14 on the platform 30. This can be useful for subsequentoperations with the plate 14.

In this embodiment of the invention, which is an embodiment for use withan automated streaking apparatus of the type identified above, the platework position A includes a notional action line B (shown by a brokenline in FIG. 1) fixed in two dimensions (x,y) in a predeterminedposition. However, and also as explained above, in some embodiments ofthe invention, where it may not be necessary to determine a line,located in three dimensional space, for the surface of a medium(represented by a line across its surface such as is illustrated as lineD in FIG. 3 for this embodiment), there will be no need forpredetermination of the notional action line B.

In this embodiment though, the notional action line B is fixed in twodimensions (x,y) in a predetermined position. This action line B isherein referred to as being a “notional” action line given that it willnot be a visible action line and also will not have a determinedposition in three dimensional space until the location of the surface 13of the medium 12 in the plate 14 is determined.

The plate work position A includes a datum level C, which in FIG. 1 isshown as the uppermost surface upon the plate platform 30 (eventually tobe located, as is evident in FIG. 2, within the plate work position A).

The apparatus 10 includes a sensor 20 that includes an ultrasonicsensing device 22 having an ultrasonic beam focusing element that iscapable of providing a focused beam on the medium surface 12, preferablywithin a sensing region (not identified in FIGS. 2 and 3) that iscentral to the predetermined notional action line B. The sensor 20 isrigidly mounted via a sensor support arm 24 to a main frame 26, therebydefining the general location of the plate work position A. In thisform, the sensor 20 is ideally mounted so that it is above the platework position A and is operatively adjacent the plate 14 heldimmediately therebelow in the plate platform 30, the plate 14 having itssurface 13 open upwardly as is evident in FIG. 3.

With reference to FIG. 3, the method of this embodiment of the presentinvention thus requires the sensor 20 to sense the medium surface 13 forthe positioned plate 14 and measure the distance to the medium surface13. Then, the measured distance is referenced to the datum level C todetermine a surface positional reference relative to the datum level Cin one dimension (z) for the surface 13 in the positioned plate 14. Inthis manner, it will be appreciated that the surface 13 can thus belocated in at least the z dimension by virtue of the determination ofthis surface positional reference. This effectively determines theheight of the medium 12 in the plate 14, at least with reference to thatdatum level C. In this respect, and as can be seen in the figures, thedatum level C is a surface that forms a part of the plate platform 30upon which the plate 14 is clamped and supported. Therefore, in thisembodiment, the determination of the surface positional referenceeffectively determines the height of the medium 12 with reference to theplate platform 30 upon which it rests.

This surface positional reference can then be used, together with thenotional action line B (from FIG. 1) to determine the line D in threedimensions (x,y,z) that is representative of a line across the surface13 in the positioned plate.

Following location of the surface in this manner, an inoculating device50 can be brought to the plate work position A to inoculate the surface12 in the manner described above. By having previously determined, bysuitable means, the location and orientation of the dispensing tip 52 onthe inoculating device 50, the dispensing tip 52 can be brought as closeas desired to the representative line D (and thus the surface 12) todispense inoculum therealong. The same benefits are of course availablefor operatively interacting a streaking device (not shown) having astreaking tool (also not shown) upon the surface 13.

As mentioned above, in an embodiment of present invention, there can beincluded the additional step of setting an upper detection limit and alower detection limit, in some forms with the upper detection limitabove the datum level C and the lower detection limit below the datumlevel C, to define a detection range between the upper and lower limits.The use of such a detection range can be adopted in conjunction witheither the method for the determination of the surface positionalreference (alone) or the method for the determination of therepresentative surface line D (as has been illustrated in FIGS. 1 to 3for this embodiment of the invention) from the surface positionalreference.

In order to assist with an explanation of the use of such a detectionrange, but also to assist with an understanding of the mathematical andgeometric processes described above, reference is made to the schematicillustration of FIG. 4 (which generally utilizes different referencenumerals to those used above for FIGS. 1 to 3).

In FIG. 4, there is shown a sensor 100 located above the surface 102 ofa medium 104 in a plate 106. The plate 106 is shown seated upright upona plate platform 108 that is used to provide a fixed datum level C. Thesensor 100 is an ultrasonic sensor that emits an acoustic signal towardsthe surface 102 via the beam 110 to form a sensing region 112.

The sensor is operated to measure the distance d to the surface 102 fromits fixed datum point 101, the distance d being calculated by the sensor100 as an average of the distances across the sensing region 112. Themeasured distance d is then referenced to the datum level C, which isthus a known distance c from the sensor 100. This referencing permitsthe determination of a surface positional reference p, relative to thedatum level C, in one dimension (z) for the surface 102 in thepositioned plate 106. In this embodiment, the surface positionalreference p is a very close approximation to the depth of the medium 104in the plate 106, due to the use of the uppermost surface of the plateplatform 108 as the datum level C, the measure only being anapproximation due to the thickness of the plate bottom.

Nonetheless, by locating the surface 102 in this manner (or by takingthe additional step of locating the surface 102 with reference to a linein three dimensions), it then becomes possible to bring to the surface102 other apparatus, such as the inoculation and streaking devicesmentioned above, such that they can engage or operatively interact withthe surface as required due to this knowledge of the location of thesurface.

Also illustrated in FIG. 4 is a detection range R having an upper limitR₁ and a lower limit R₂, which have been set arbitrarily at levels aboveand below the datum level C. In this respect, it will be appreciatedthat the detection range R could have been arbitrarily set at levelsr₁and r₂ for a situation where it is not necessary or desirable todetermine if, for example, the plate 106 still included its lid thereon,or perhaps had been placed on the platform 108 empty of medium. In thatsituation, and with such a narrow detection range, where the upper limitr₁ is only just above the surface 102 and the lower limit r₂ is onlyjust below the surface 102, the sensor 100 will not function if thedetectable upwardly exposed surface of a plate is outside this narrowrange, due to the sensor 100 detecting either the surface of the platelid or the surface of the plate bottom.

However, in this embodiment, it is desirable to provide an alarm in bothof these situations and thus a relatively broad enough detection range Rhas been set.

Thus, in this embodiment, the sensor 100 is able to sense the presenceof the lid wall or the bottom wall as they will be within the detectionrange set by the upper limit R₁ and the lower limit R₂, and will measurethe distance to that surface rather than to the surface of the medium inthe plate. By the provision of calibration sub-ranges between r₁ and R₁and between r₂ and R₂, such calibration sub-ranges can cause theidentification (by virtue of the determination of the surface positionalreference and its presence in one of the alarm calibration sub-ranges)of an alarm condition, as well as allowing for the proper functioning ofthe method.

In conclusion, it must be appreciated that there may be other variationsand modifications to the configurations described herein which are alsowithin the scope of the present invention.

1. A method for locating the surface of a solid growth culture medium ina plate in a plate work position, the plate work position including asensor and having a datum level fixed in one dimension (z), the methodincluding: placing the plate in the plate work position; using thesensor to sense the medium surface for the positioned plate andmeasuring the distance to the medium surface; and referencing themeasured distance to the datum level to determine a surface positionalreference, relative to the datum level, in one dimension (z) for thesurface of the medium in the positioned plate.
 2. A method according toclaim 1, wherein the surface of a medium in a plate, which plate is inits normal, generally horizontal orientation, is located in at least thez dimension by virtue of the determination of the surface positionalreference.
 3. A method according to claim 1, wherein the datum level isa surface that forms a part of a plate platform upon which the plate canbe clamped and supported.
 4. A method according to claim 1, wherein thedetermination of the surface positional reference determines the heightof the medium with reference to the plate platform upon which it rests.5. A method according to claim 1, wherein the medium is sensed in asensing region, such that the measured distance is an average over thearea of the sensing region.
 6. A method for locating the surface of asolid growth culture medium in a plate in a plate work position, theplate work position including a sensor and having a notional action linefixed in two dimensions (x,y) in a predetermined position and having adatum level fixed in one dimension (z), the method including: placingthe plate in the plate work position; using the sensor to sense themedium surface within a sensing region for the positioned plate andmeasuring an average distance to the medium surface within that sensingregion; referencing the measured distance to the datum level todetermine a surface positional reference relative to the datum level inone dimension (z) for the surface of the medium in the positioned plate;and using the surface positional reference and the notional action lineto determine a line in three dimensions (x,y,z) that is representativeof a line across the surface of the medium in the positioned plate.
 7. Amethod for locating the surface of a solid growth culture medium in aplate in a plate work position, the plate work position including asensor and having a datum level fixed in one dimension (z), the methodincluding: setting an upper limit and a lower limit to define adetection range between the upper and lower limits; placing the plate inthe plate work position; using the sensor to sense, within the detectionrange, the medium surface for the positioned plate and measuring thedistance to the medium surface; and referencing the measured distance tothe datum level to provide a surface positional reference relative tothe datum level in one dimension (z) for the surface of the medium inthe positioned plate.
 8. A method according to claim 7, wherein theupper detection limit is above the datum level and the lower detectionlimit is below the datum level.
 9. A method according to claim 7,wherein the detection range is provided with calibration sub-ranges. 10.A method according to claim 9, wherein the calibration sub-rangesidentify alarm conditions.
 11. A method according to claim 10, whereinthe alarm conditions are where a plate positioned in the plate workposition still includes its lid thereon or has been placed in the platework position upside down.
 12. A method according to claim 11, whereinthe detection range is set at about 30 mm, with the upper limit set 20mm above the datum level and the lower limit set 10 mm below the datumlevel.
 13. A method for locating the surface of a solid growth culturemedium in a plate in a plate work position, the plate work positionincluding a sensor and having a notional action line fixed in twodimensions (x,y) in a predetermined position and having a datum levelfixed in one dimension (z), the method including: setting an upper limitand a lower limit to define a detection range between the upper andlower limits; placing the plate in the plate work position; using thesensor to sense the medium surface, within the detection range, within asensing region for the positioned plate and measuring an averagedistance to the medium surface within that sensing region; referencingthe measured distance to the datum level to determine a surfacepositional reference relative to the datum level in one dimension (z)for the surface of the medium in the positioned plate; and using thesurface positional reference and the notional action line to determine aline in three dimensions (x,y,z) that is representative of a line acrossthe surface of the medium in the positioned plate.
 14. A methodaccording to claim 1, wherein the sensor is an ultrasonic sensing devicethat includes an ultrasonic beam focusing element that is capable ofproviding a focused beam on the medium surface.
 15. A method accordingto claim 1, wherein the sensor is rigidly mounted to a main frame,thereby defining the general location of the plate work position.
 16. Amethod according to claim 1, wherein the sensor is mounted to be abovethe plate work position and operatively adjacent a positioned plate heldimmediately therebelow in a plate platform, the positioned plate havingits medium surface open upwardly.
 17. An apparatus for locating thesurface of a solid growth culture medium in a plate in a plate workposition, the plate work position including a sensor and also having adatum level fixed in one dimension (z), wherein the sensor is capable ofsensing the medium surface for the positioned plate and measuring thedistance to the medium surface, the apparatus also including means forreferencing the measured distance to the datum level to determine asurface positional reference, relative to the datum level, in onedimension (z) for the surface of the medium in the positioned plate. 18.An apparatus for locating the surface of a solid growth culture mediumin a plate in a plate work position, the plate work position including asensor and having a notional action line fixed in two dimensions (x,y)in a predetermined position and having a datum level fixed in onedimension (z), wherein the sensor is capable of sensing the mediumsurface within a sensing region for the positioned plate and measuringan average distance to the medium surface within that sensing region,the apparatus also including means for referencing the measured distanceto the datum level to determine a surface positional reference relativeto the datum level in one dimension (z) for the surface of the medium inthe positioned plate and then using the surface positional reference andthe notional action line to determine a line in three dimensions (x,y,z)that is representative of a line across the surface of the medium in thepositioned plate.
 19. An apparatus for locating the surface of a solidgrowth culture medium in a plate in a plate work position, the platework position including a sensor and having a datum level fixed in onedimension (z), wherein the sensor has an upper limit and a lower limitto define a detection range between the upper and lower limits, and iscapable of sensing, within the detection range, the medium surface forthe positioned plate and measuring the distance to the medium surface,the apparatus including means for referencing the measured distance tothe datum level to provide a surface positional reference relative tothe datum level in one dimension (z) for the surface of the medium inthe positioned plate.
 20. An apparatus for locating the surface of asolid growth culture medium in a plate in a plate work position, theplate work position including a sensor and having a notional action linefixed in two dimensions (x,y) in a predetermined position and alsohaving a datum level fixed in one dimension (z), wherein the sensor hasan upper limit and a lower limit to define a detection range between theupper and lower limits, and is capable of sensing the medium surface,within the detection range, within a sensing region for the positionedplate and measuring an average distance to the medium surface withinthat sensing region, the apparatus including means for referencing themeasured distance to the datum level to determine a surface positionalreference relative to the datum level in one dimension (z) for thesurface of the medium in the positioned plate, and then using thesurface positional reference and the notional action line to determine aline in three dimensions (x,y,z) that is representative of a line acrossthe surface of the medium in the positioned plate.
 21. An apparatusaccording to claim 17, wherein the sensor is an ultrasonic sensingdevice that includes an ultrasonic beam focusing element that is capableof providing a focused beam on the medium surface.
 22. An apparatusaccording to claim 17, wherein the sensor is rigidly mounted to a mainframe, thereby defining the general location of the plate work position.23. An apparatus according to claim 17, wherein the sensor is mounted tobe above the plate work position and operatively adjacent a positionedplate held immediately therebelow in a plate platform, the positionedplate having its medium surface open upwardly. 24-31. (canceled)